Maybe it is, and it's not 'pure', but I wanted some more light. I may try increasing exposure, as I find a default PT render pretty dark. It's possible in post too, no doubt. I have also found that some of my renders have been printed very dark (in books), compared to what I see on my monitor, but that may be a printer's error.

The default exposure and sunlight are tweaked for a more open scene and are not ideal for this kind of dappled sunlight scene. I would treat this like photography and solve it by increasing exposure. That's what you'd have to do with a real camera in this scene, and it's also what your eyes would do naturally if you were standing there. You might overexpose the parts in sunlight, but personally I don't mind that. There may be ways to avoid that. You could lighten up the sky to get more light into the shadows. And maybe brighten up the materials in the scene so that they bounce more light around.

Here's another iteration (70% of rendersize). Exposure now set to 1.3, no extra sun, robust sampling (1/256), and shadows of objects in low cloud checked. I tried the contrast setting, but it became a bit too flat, so I changed it to 0.25 again.This was actually a test of a Megascan forest floor tiled texture, but as usual, I built it up a bit.